Many biologically active substances, for example, hormones, neurotransmitters and peptides are known to exert functions via intracellular mediators such as, cyclic adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP), diacylglycerol (DAG) and calcium. In many cases, these mediators activate or inactivate intracellular kinases or phosphatases that are important in protein phosphorylation/dephosphorylation, and thus play important roles in regulating cellular processes and functions. The protein kinase C (PKC) family of calcium and/or lipid-activated serine-threonine kinases function downstream of nearly all membrane-associated signal transduction pathways.1 Approximately 12 different isozymes comprise the PKC family, which are broadly classified by their activation characteristics. The conventional PKC isozymes (PKCα, βI, βII, and γ) are calcium- and lipid-activated, while the novel isozymes (ε, θ, η, and δ) and atypical isozymes (ζ, ι, υ, and μ) are calcium independent but activated by distinct lipids.2 For example, stimulation of Gαq-coupled G-protein coupled receptors (GPCR) can activate phospholipase C (PLC) which in turn mediates hydrolysis of inositol phospholipids resulting in the generation of inositol 1,4,5-triphosphate (IP3) and DAG. IP3 and DAG can activate the different isoforms of PKC by mobilizing calcium (calcium sensitive enzymes) or by directly activating PKC, respectively. Once activated, PKC isozymes translocate to discrete subcellular locations through direct interactions with docking proteins termed RACKs (Receptor for Activated C Kinases), which permit specific substrate recognition and subsequent signal transduction.3 
Alterations in PKC activity has been suggested to contribute to human diseases, inter alia, diabetes, numerous forms of cancer, microalbinuria, endothelial dysfunction, cerebrovascular disease, stroke, coronary heart disease, cardiovascular disease and sequela (e.g. arrhythmia, sudden death, increased infarct size, congestive heart failure, angina), myocardial ischemic states, hypertension, lipid disorders, ischemia-reperfusion injury, atherosclerosis, peripheral artery/vascular disease, microvascular complications of diabetes (neuropathy, nephropathy, retinopathy), restenosis, renal disease, blood coagulation disorders, inflammatory diseases and heart failure and inhibition of PKC in these settings could be used to treat or prevent human disease. Lending support to the modulation of PKC in cardiac disease, PKC activation has been associated with cardiac hypertrophy, dilated cardiomyopathy, ischemic injury and mitogen stimulation.
Heart disease is the leading cause of death in industrialized nations. Historically heart failure (HF) has been a product of hypertension, coronary heart disease, genetic disorders, valvular deformities, diabetes or cardiomyopathy. While the root cause of heart failure is multifaceted, it uniformly is marked by impaired diastolic and/or systolic function and can be accompanied by chamber enlargement which ultimately manifest in symptomatic heart failure (fatigue, pulmonary edema, circulatory congestion, etc.)
The risk of death due to heart failure is 5-10% annually in patients with mild symptoms of heart failure, and increases to 30-40% annually in patients with advanced heart failure, with a 50% overall mortality rate at 5 years. The current mainstays of heart failure therapy are drugs that act on the renin-angiotensin-aldosterone system (ACEI, ARB, aldosterone inhibitor), diuretics, digoxin and β-adrenergic receptor blockers. Despite the fact that multiple drug classes are used to treat heart failure patients, new cases of heart failure are growing at over 10% per year.
Patients with acute decompensated heart failure (ADHF) are a treatment challenge to physicians and can present with volume overload and/or diminished cardiac output. Initial treatments for ADHF patients include intravenous diuretics, vasodilators, natriuretic peptides and inotropic agents. Despite the widespread use of these agents, long-term safety and benefit of these drugs have been questioned. In the case of inotropes, drugs that increase cardiac output and cardiac contractility without increasing myocardial oxygen consumption or heart rate are desirous. Despite the available treatments for patients with ADHF, hospital readmission rates are approximately 50% within 6 months and mortality is approximately 20-40% at 1 year.
The primary function of the heart is to generate and sustain an arterial blood pressure necessary to provide adequate perfusion of organs. It has, therefore, become an area of intense investigation to decipher the mechanism(s) which initiate and contribute to the development of heart failure rather than relying on a means for treating the symptoms of heart failure alone. At the cardiomyocyte (cardiac contractile cells) level, impaired calcium cycling is a hallmark of heart failure as is the basis of contractile abnormalities. Calcium plays a key role in regulating kinases, phosphatases and transcription factors believed to influence the remodeling process indicating that both acute and sustained alterations in intracellular calcium levels may have profound effect on cardiac function and remodeling (i.e., changes in wall thickness or chamber volume). This theory would support the proposition that the development of new therapies addressing the slowing and preventing of the disease progression, would be perhaps more effective against heart failure than palliation of heart failure.
Therefore, there is a limited means to treat patients with various forms and stages of heart failure and there is incentive to develop novel, safe and effective treatments to prevent or treat patients with symptoms of heart failure, acute exacerbation of heart failure and chronic heart failure and other cardiovascular diseases. An agent that has benefits in the treating acute exacerbations of heart failure as well as treating chronic heart failure is desirous.    1. Molkentin et al. (2001) Annu. Rev. Physiol. 63:391-426.    2. Dempsey et al. (2000) Am. J. Physiol. Lung Mol. Physiol. 279:247-251.    3. Mochly-Rosen, D. (1995) Science 268:247-251.